Over the past two decades or so, a variety of disposable absorbent products have been widely marketed for use as disposable baby and adult diapers, underpads, hospital bed pads, feminine napkins, and so forth. These products largely consist of laminates of one or more layers of tissue-like material incorporating a layer of liquid absorbing agent. Typically, these laminates are constructed of a nonwoven cover sheet, an absorbent center section and a water impermeable backing sheet to entrain moisture within the disposable absorbent product.
In recent years, a variety of hydrocolloidal polymers, often referred to as superabsorbents, have been incorporated into these laminates for disposable absorbent products. Prior to the incorporation of superabsorbents, it was common to incorporate tissue-like cellulose and other bulky, water absorbing materials to absorb body fluids. Superabsorbents have been used to replace at least a portion of the cellulosic materials primarily because these polymeric components have an ability to absorb larger quantities of liquids, thereby enhancing the effectiveness of the disposable product. Another factor leading to their use is their ability to retain moisture under pressure as might be experienced when a child sits on the absorbent medium. Cellulose, waddings and fluff pulp tend to fail under those pressure conditions.
The introduction of superabsorbents into the disposable absorbent product market has not been without problems. The superabsorbents are dusty thus making it difficult for handling and storage and tend to shift within the finished product. Shifting of the superabsorbent presents two problems, first the superabsorbent may shift from the point where it is most needed in the product and second, shifting allows the superabsorbents to agglomerate within the product. When the superabsorbents become wet, they agglomerate and display a tendency to generate a gelatinous barrier film which detracts from the ability of the superabsorbent to absorb fluids. To overcome shifting of the superabsorbents within these laminates for disposable absorbent soft goods, a variety of methods have been developed to retain the superabsorbents in fixed location within the laminates incorporated into the disposable absorbent soft goods. Typically, these methods of retaining the superabsorbents within a fixed position within the laminates (typically the fixed locations have been in the shape of squares, rectangles, and triangles) have involved the application of a variety of adhesives, the use of hot melts, specialty fibers, or superabsorbents which are moisture activated, to anchor the superabsorbent between fibrous facing sheets.
The following patents are representative of various techniques for preparing a variety of disposable absorbent soft goods and fixing superabsorbents and hydrocolloidal polymers within the disposable product.
U.S. Pat. No. 4,102,340 discloses an absorbent article, such as a diaper or sanitary napkin, comprised of a facing sheet, an absorbent pad means and a moisture-impervious backing sheet. The absorbent pad comprises a fibrous structure having an intermediate, densified layer and a layer of highly porous, loosely compacted bats on each side of the densified layer, the bat incorporating particulate water insoluble and water swellable polymeric absorbents. The facing sheet is comprised of a cellulosic material incorporating a self-crosslinking acrylic emulsion bonding agent to supply strength to the cellulosic substrate such that when the disposable product is wet it retains dimensional stability. In practice, the absorbent pad is disposed between the moisture impervious backing, and the facing sheet and then bonded to the moisture-impervious backing sheet by means of adhesive beads.
European 0 202 472 discloses non-laminated, dry formed absorbent products formed by an air-laying technique. More particularly, the absorbent products are formed in dry condition, a sheet or web from matrix fibers or mixture of cellulosic and synthetic fibers distributing among the matrix fibers a superabsorbent material and a heat-activated binder such as polyvinyl acetate, vinyl acetate, ethylene and vinyl chloride, etc., which, upon the application of heat, thermally sets to bind the matrix fibers and liquid absorbing material into a coherent web.
U.S. Pat. No. 4,260,443 discloses a process for producing disposable absorbent goods which comprises forming a laminated sheet composed of two or more layers of tissue having a water-absorbing polymer, e.g., a superabsorbent, fixed in place between the layers. When the tissue sheets are passed through an embossing roll, a small amount of water is applied to all or a percentage of the embossed area which causes the superabsorbent to become tacky and act as an adhesive at these locations thereby securing the tissue sheets together. After the resulting laminate has passed through the embossing roll, the laminating sheet is dried.
U.S. Pat. No. 3,575,749 discloses a method for making fibrous sheets or web by incorporating a binder such as starch or starch derivative, acrylic or butadiene/styrene emulsions, etc. into the fibrous material. The fiber layer to which the binder has been applied is made plastic by applying moisture. During an embossing operation where the fibers are brought into intimate contact with each other followed by drying of the product, the partly plasticized binder is cured, thereby effecting a strong bond.
U.S. Pat. No. 5,273,596 discloses a method for producing disposable absorbent pads employing a multi-layer, nonwoven fabric for use as a top sheet. The multi-layer, fabric is comprised of a continuous first layer of about 75% hydrophobic thermoplastic fibers and a second layer comprised of a blend of hydrophobic and hydrophilic fibers. The layers are secured by bonds which are formed by melt-fusing portions of the hydrophobic thermoplastic fiber.
U.S. Pat. No. 5,415,717 discloses an apparatus for depositing particles on a moving web of materials. In the process, a web is conveyed by means of a belt and particulate material, e.g., a superabsorbent, is deposited upon the web. As the web is conveyed along the belt, it is brought into contact with a second web and the second web is caused to overlap the particulate particles. The first and second webs then are compressed beneath rollers and the particles caused to be locked into a fixed position through the use of binder coatings or spray adhesives.
U.S. Pat. No. 5,370,764 discloses a process for producing film-laminated material employing a nonwoven web formed by a variety of processes such as spun bonding, air laying, wet laying, dry laying, etc. The laminates incorporate a moisture-absorbing medium and, when brought into contact with another web, are embossed to form spaced apart bonding regions. Bonding is effected via thermal means, e.g., heated rollers and the like.